1. Field of the Invention
The present invention relates to a manufacturing method of a semiconductor device having a gate electrode such as mainly a MOS transistor.
2. Description of the Related Art
In order to fabricate multiple types of MOS transistors having different driving voltages on the same substrate, gate insulating films of the respective MOS transistors should be formed to have predetermined different film thicknesses. Here, there is exemplified a case in which two types of MOS transistors, that is, MOS transistors for two power supplies, are fabricated.
First, after a first gate insulating film is formed above a semiconductor substrate (or semiconductor layer), a resist pattern is formed on this first gate insulating film, and with this resist pattern being a mask, the first gate insulating film is processed by etching so that a predetermined portion of the first gate insulating film is removed. Here, as the etching of the first gate insulating film, common dry etching is not adequate but wet etching using, for example, an HF solution as an etching solution is suitable, since the gate insulating film is quite thin and vulnerable to damage. Then, by forming a second gate insulating film on the entire surface, there are formed a first region of only the second gate insulating film and a second region in which the first and second gate insulating films are stacked. There are formed a first gate electrode for low voltage drive in the first region, and a second gate electrode for high voltage drive in the second region.
Incidentally, in a case of three or more power supplies, there should be repeated steps of further stacking a gate insulating film, etching it to the first gate insulating film, and stacking and forming a gate insulating film again.
(Patent Document 1) Japanese Patent Application Laid-open No. 2004-336003
(Patent Document 2) Japanese Patent Application Laid-open No. 2003-209121
(Patent Document 3) Japanese Patent Application Laid-Open No. 2001-307984
However, as the gate insulating film gets further thinner, deterioration of film quality which is considered to be due to damage by the step after formation of the gate insulating film is beginning to be regarded as a problem.